The present invention relates to an improved method for providing a resin bonded joint having substantially resin free surfaces adjacent to the joint, thereby enhancing secondary bonding on the adjacent surfaces. This improved method finds particular utility for bonding structural members used in aircraft where the tolerance for misalignment from residual resin deposits is slight.
Typically, when structural members are bonded, excessive adhesive or resin, commonly referred to as flash, tends to bleed from a joint between the bonded members and onto surfaces adjacent to the joint. FIG. 1 depicts a structure having one doubler member 10, bonded together to a lower member 12, along a resin layer 14. A first side 16 reflects the typical spreading of flash 18 along exterior surfaces ajacent the adhesive layer 14 resulting from application of pressure during the bonding operation.
The flash 18 shown on the first side 16 of the bonded members 10, 12 is commonly removed by machining or grinding the excess adhesive coated on the exterior surfaces of the bonded members 10, 12, because such excess resin may have a significant impact on overall weight and stability. In addition to the obvious time considerations, such corrective measures increase the risk of further error, which may be unacceptable for many applications, particularly those requiring a high degree of precision.
A conventional method for removing the flash is shown on a second side 20 of the bonded doubler member 10 and lower member 12. According to this method, a flash breaker (i.e., tape) 19 is extended along the surface of the lower member 12 adjacent to the doubler member 10 and the resin layer 14. The flash breaker 19 collects the flash 18 and the flash breaker 19 is then stripped from the surface of the lower member 12 to remove the flash.
The conventional method illustrated on the second side 20 of FIG. 1 is unsatisfactory. According to this technique, as the flash breaker 19 is removed from member 12, particles of tape 19a remain as do particles of flash l8a which must also be removed by machining or grinding though not as much as shown on side 16, since bonding materials oftentimes will not adhere to contaminated surfaces during rebonding. Occasionally, the flash breaker tape 19a flows under the doubler member 10 and is trapped resulting in major rework requiring the removal of the doubler member 10, reprocessing, and re-bonding. This rework is time consuming and greatly increases cost.
Another conventional method of removing adhesive flash 18 is shown in FIG. 2. In accordance with this method, a teflon-coated fiberglass fabric sheet 28 and an absorbent material 30 are extended over the upper and lower bonded members 11a, 11b. The fiberglass fabric sheet 28, while absorbing a small amount of flash, causes the flash to bridge, as depicted by the reference numeral 18b in FIG. 2. The bridged flash 18b also must be removed by machining to provide a suitable, adhesive free surface. As an alternative to this method, a highly compacted absorbing material in the shape of a gasket may be extended over the fiberglass sheet 28 and around the periphery of the bonded members. This alternative is costly, time consuming, and impractical depending on the configuration of the bonded structures.